1. Field of the Invention
The present invention relates to an improved interstitial heat applicator whereby a local area of human or animal living tissue is heated by electromagnetic radiation.
2. Discussion of Background
Prior art microwave interstitial applicators utilize a conductor with a gap in the outer conductor. These type of structures invariably experience difficulty with respect to the energy which is radiated from the gap in the outer conductor of the applicator. Primarily, the difficulty is the travelling of the energy back along the surface of the outer conductor toward the input at the air-tissue interface. When this type of energy, which is radiated back along the outer conductor, is experienced, a heating pattern is developed so that heating occurs at the insertion point of the applicator. This is usually an undesirable result which in the very least detracts from the applicator's effectiveness and which creates not only a loss of heat at the point at which it is desired to be used but also provides an unintended heat "spot" where such heat spot is either uncomfortable or harmful. The harmful effects become more pronounced as higher power levels are used in order to heat localized growths by using a single applicator.
One type of prior art solution to this problem is disclosed in U.S. Pat. No. 4,448,198 wherein the applicators are provided with a "interconnecting means" in such a configuration so as to cause constructive interference within the emitted electromagnetic radiation when the applicators are inserted into the body tissue in a preselected spaced apart relationship. In a particular embodiment a plurality of parallel spaced applicators are placed in conjunction with an interconnecting means including a line stretcher to vary the phase of the electromagnetic energy provided to each applicator. Additionally, a catheter and a hypodermic needle are provided for inserting and positioning each applicator into the body tissue in a spaced apart relationship.
This and other prior art attempts to deal with these type of invasive hypothermia situations fail to provide accurate control of the applied power. That is, although the pattern of energy radiated from the gap and the outer conductor has been modified in the prior art with respect to its backward travel to the surface of the air-tissue interface, such modification is adapted to the particular situation and requires extensive modification for a different environment. Furthermore, the control of the spotting of the maximum heat is not at all precise and is not able to be duplicated from one application to another because of changing conditions and orientation.